html {
    font-size: 12px;
    background-image: url(./img/wallhaven-567530.jpg);
    background-size: cover;
    background-position: center center;
    background-repeat: no-repeat;
}

html,
body {
    margin: 0;
    padding: 0;
    font-family: sans-serif;
}

.keys {
    display: flex;
    flex: 1; /* 使元素占满屏 */
    min-height: 100vh; /* 使元素占满屏 */
    align-items: center; /* 使元素垂直居中 */
    justify-content: center; /* 使元素水平居中 */
}

.key {
    border: 4px solid #fbd8b2;
    border-radius: 5px;
    width: 100px;
    margin: 1rem;
    padding: 1rem 0.5rem;
    font-size: 1.5rem;
    text-align: center;
    color: white;
    background-color: rgba(0, 0, 0, 0.1);
    text-shadow: 0 0 5px #ff3600;
    transition: all 0.07s;
}

kbd {
    display: block; /* 使 A-L 占一行 */
    font-size: 40px;
}

.sound {
    font-size: 1.2rem;
    text-transform: uppercase; /* 使说明文字 clap 等转为大写 */
    letter-spacing: 5px; /* 字母间距 */
    color: #52281c;
}

.playing {
  transform: scale(1.3); /* 当被点击时，对应方框放大 */
  border-color: #ffc600; /* 当被点击时，对应方框的边框变色 */
  box-shadow: 0 0 10px #ffc600;
}
